Carbonated beverages range in variety from carbonated water, knows as soda water or sparkling water, to a carbonated water flavored with natural or artificial flavors such as orange, lemon-lime, cola, and many more.
The amount of carbon dioxide gas dissolved into these products is usually referred to as Volume of CO.sub.2 per Volume of Liquid. The higher the volume of CO.sub.2 per unit Volume of Liquid, the greater the sparkle and effervescence of the beverage. Although the desirable level of carbonation in a beverage is a matter of personal preference, packaged soft drinks are usually made with 3.5 to 4.0 volumes of carbon dioxide for colas, 4.0 to 5.0 Volumes of CO.sub.2 for seltzers and soda water and generally less that 3.0 volumes for orange flavor. One of the disadvantages of packaged carbonated beverages is that the carbonation level is fixed and not available at different levels to suit different personal tastes.
Other disadvantages of packaged carbonated beverages include the unnecessary cost of packaging and transportation of a product that is comprised essentially of water and the cost of disposal or recycling of the package. Still further is the problem that once the pressurized beverage container is open to the atmosphere, the beverage left unconsumed and unpressurized tends to lose carbonation and go flat thus wasting the unconsumed portion.
Several products have been developed to overcome the above noted problems and make possible the preparation of carbonated beverages in the home. Many of these products are described in several prior art patents discussed in our prior U.S. Pat. No. 5,260,081 and for the sake of brevity, these patents will not be repeated in this specification.
One of these prior patents which should be mentioned, however, is U.S. Pat. No. 4,040,342 (Austin), which discloses a gas generating chamber with a gas conduit extending into a carbonating chamber. After the chemical reaction is activated, the carbon dioxide flows into the carbonating chamber and carbonates the liquid contained therein. There are several limitations and problems with this device.
First, the time required to carbonate the liquid to 3 or more Volumes of CO.sub.2 is fifteen minutes or greater. This is because the process of dissolving carbon dioxide into liquid occurs in two mechanisms; one quite rapid and the other quite slow. Some of the gas dissolves into the liquid as it bubbles to the surface and fills the head space of the carbonation tank. This CO.sub.2 solution process occurs quite rapidly though it is, of course, dependent upon the rate of the chemical reaction producing the CO.sub.2. Pressurized CO.sub.2 in the head space acting upon the surface of the liquid is the other gas absorption mechanism. This absorption rate is slow because of the fixed interfacial exposure area between the CO.sub.2 and the liquid. If this interfacial exposure area could be increased by agitation or by turbulent mixing as is taught by U.S. Pat. No. 4,719,056 (Scott) then CO.sub.2 absorption would occur far more rapidly.
The other problem is the likely occurrence of transfer of some of the salt by-products of the CO.sub.2 generation reaction into the liquid to be carbonated.
The reaction of edible acids (such as citric) with carbonates (such as sodium bicarbonate) in an aqueous solution is an endothermic reaction. When the reaction is first initiated, therefore, it is at its maximum temperature and its fastest reaction rate. In addition, the maximum amount of fuel for the reaction is present when it first begins. Therefore, during its initial stages the reaction produces considerable foaming and surface effervescence releasing a mist of reactant salt spray into the carbon dioxide gas being generated. This salt mist enters the carbonation chamber and ultimately the liquid being carbonated.
If hot water is used as the reactant water, the reaction rate is accelerated even further and salt contamination increases further.
For improved consumer convenience, the direct carbonation of premixed beverage is more desirable than the carbonation of unflavored water to which a flavoring must be added with each serving of soda water dispensed. With the Austin apparatus, U.S. Pat. No. 4,040,342, direct carbonation of premixed beverages would not be practical because premix flavoring syrups typically contain sugar and other ingredients that sufficiently alter the surface tension of the water syrup mix to cause the mixture to foam profusely; thus expelling much of the carbonation as it is dispensed from the pressurized carbonation vessel into a receptacle at atmospheric pressure. Most commercial soda fountains meter and mix flavoring syrup into the carbonated water after the water is dispensed from the pressurized carbonation vessel; therefore, when the syrup and carbonated water are combined, they are at atmospheric pressured (a process know in the industry as "post mix") and the foaming problem is avoided.
Three U.S. Patents which should be mentioned are U.S. Pat. Nos. 4,458,584 (Annese et al.), 4,466,342 (Basile et al.) and 4,475,448 (Shoaf et al.) These patents are all closely related to each other and describe a carbonation device in which a beverage container has a separate compartment inserted therein for holding carbon dioxide producing chemicals and a separate quantity of water is added to the chemicals before closing the lid to generate carbon dioxide gas for carbonation of a liquid beverage in the container. The containers in the above three patents do not have an overpressure relief valve, are not capable of withstanding the higher carbonation pressures generated by the present invention and would provide slower carbonation than the present invention. The present invention is easier to operate since the chemical reaction is started after closing the lid rather than while the lid is open.